#!/bin/bash
#
# https://github.com/Nyr/openvpn-install
#
# Copyright (c) 2013 Nyr. Released under the MIT License.


# Detect Debian users running the script with "sh" instead of bash
if readlink /proc/$$/exe | grep -q "dash"; then
  echo 'This installer needs to be run with "bash", not "sh".'
  exit
fi

# Discard stdin. Needed when running from an one-liner which includes a newline
read -N 999999 -t 0.001

# Detect OpenVZ 6
if [[ $(uname -r | cut -d "." -f 1) -eq 2 ]]; then
  echo "The system is running an old kernel, which is incompatible with this installer."
  exit
fi

# Detect OS
# $os_version variables aren't always in use, but are kept here for convenience
if grep -qs "ubuntu" /etc/os-release; then
  os="ubuntu"
  os_version=$(grep 'VERSION_ID' /etc/os-release | cut -d '"' -f 2 | tr -d '.')
  group_name="nogroup"
elif [[ -e /etc/debian_version ]]; then
  os="debian"
  os_version=$(grep -oE '[0-9]+' /etc/debian_version | head -1)
  group_name="nogroup"
elif [[ -e /etc/almalinux-release || -e /etc/rocky-release || -e /etc/centos-release ]]; then
  os="centos"
  os_version=$(grep -shoE '[0-9]+' /etc/almalinux-release /etc/rocky-release /etc/centos-release | head -1)
  group_name="nobody"
elif [[ -e /etc/fedora-release ]]; then
  os="fedora"
  os_version=$(grep -oE '[0-9]+' /etc/fedora-release | head -1)
  group_name="nobody"
else
  echo "This installer seems to be running on an unsupported distribution.
Supported distros are Ubuntu, Debian, AlmaLinux, Rocky Linux, CentOS and Fedora."
  exit
fi

if [[ "$os" == "ubuntu" && "$os_version" -lt 1804 ]]; then
  echo "Ubuntu 18.04 or higher is required to use this installer.
This version of Ubuntu is too old and unsupported."
  exit
fi

if [[ "$os" == "debian" && "$os_version" -lt 9 ]]; then
  echo "Debian 9 or higher is required to use this installer.
This version of Debian is too old and unsupported."
  exit
fi

if [[ "$os" == "centos" && "$os_version" -lt 7 ]]; then
  echo "CentOS 7 or higher is required to use this installer.
This version of CentOS is too old and unsupported."
  exit
fi

# Detect environments where $PATH does not include the sbin directories
if ! grep -q sbin <<< "$PATH"; then
  echo '$PATH does not include sbin. Try using "su -" instead of "su".'
  exit
fi

if [[ "$EUID" -ne 0 ]]; then
  echo "This installer needs to be run with superuser privileges."
  exit
fi

if [[ ! -e /dev/net/tun ]] || ! ( exec 7<>/dev/net/tun ) 2>/dev/null; then
  echo "The system does not have the TUN device available.
TUN needs to be enabled before running this installer."
  exit
fi

new_client () {
  # Generates the custom client.ovpn
  {
  cat /etc/openvpn/server/client-common.txt
  echo "<ca>"
  cat /etc/openvpn/server/easy-rsa/pki/ca.crt
  echo "</ca>"
  echo "<cert>"
  sed -ne '/BEGIN CERTIFICATE/,$ p' /etc/openvpn/server/easy-rsa/pki/issued/"$client".crt
  echo "</cert>"
  echo "<key>"
  cat /etc/openvpn/server/easy-rsa/pki/private/"$client".key
  echo "</key>"
  echo "<tls-crypt>"
  sed -ne '/BEGIN OpenVPN Static key/,$ p' /etc/openvpn/server/tc.key
  echo "</tls-crypt>"
  } > ~/"$client".ovpn
}

if [[ ! -e /etc/openvpn/server/server.conf ]]; then
  # Detect some Debian minimal setups where neither wget nor curl are installed
  if ! hash wget 2>/dev/null && ! hash curl 2>/dev/null; then
    echo "Wget is required to use this installer."
    read -n1 -r -p "Press any key to install Wget and continue..."
    apt-get update
    apt-get install -y wget
  fi
  clear
  echo 'Welcome to this OpenVPN road warrior installer!'
  # If system has a single IPv4, it is selected automatically. Else, ask the user
  if [[ $(ip -4 addr | grep inet | grep -vEc '127(\.[0-9]{1,3}){3}') -eq 1 ]]; then
    ip=$(ip -4 addr | grep inet | grep -vE '127(\.[0-9]{1,3}){3}' | cut -d '/' -f 1 | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}')
  else
    number_of_ip=$(ip -4 addr | grep inet | grep -vEc '127(\.[0-9]{1,3}){3}')
    echo
    echo "Which IPv4 address should be used?"
    ip -4 addr | grep inet | grep -vE '127(\.[0-9]{1,3}){3}' | cut -d '/' -f 1 | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}' | nl -s ') '
    read -p "IPv4 address [1]: " ip_number
    until [[ -z "$ip_number" || "$ip_number" =~ ^[0-9]+$ && "$ip_number" -le "$number_of_ip" ]]; do
      echo "$ip_number: invalid selection."
      read -p "IPv4 address [1]: " ip_number
    done
    [[ -z "$ip_number" ]] && ip_number="1"
    ip=$(ip -4 addr | grep inet | grep -vE '127(\.[0-9]{1,3}){3}' | cut -d '/' -f 1 | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}' | sed -n "$ip_number"p)
  fi
  # If $ip is a private IP address, the server must be behind NAT
  if echo "$ip" | grep -qE '^(10\.|172\.1[6789]\.|172\.2[0-9]\.|172\.3[01]\.|192\.168)'; then
    echo
    echo "This server is behind NAT. What is the public IPv4 address or hostname?"
    # Get public IP and sanitize with grep
    get_public_ip=$(grep -m 1 -oE '^[0-9]{1,3}(\.[0-9]{1,3}){3}$' <<< "$(wget -T 10 -t 1 -4qO- "http://ip1.dynupdate.no-ip.com/" || curl -m 10 -4Ls "http://ip1.dynupdate.no-ip.com/")")
    read -p "Public IPv4 address / hostname [$get_public_ip]: " public_ip
    # If the checkip service is unavailable and user didn't provide input, ask again
    until [[ -n "$get_public_ip" || -n "$public_ip" ]]; do
      echo "Invalid input."
      read -p "Public IPv4 address / hostname: " public_ip
    done
    [[ -z "$public_ip" ]] && public_ip="$get_public_ip"
  fi
  # If system has a single IPv6, it is selected automatically
  if [[ $(ip -6 addr | grep -c 'inet6 [23]') -eq 1 ]]; then
    ip6=$(ip -6 addr | grep 'inet6 [23]' | cut -d '/' -f 1 | grep -oE '([0-9a-fA-F]{0,4}:){1,7}[0-9a-fA-F]{0,4}')
  fi
  # If system has multiple IPv6, ask the user to select one
  if [[ $(ip -6 addr | grep -c 'inet6 [23]') -gt 1 ]]; then
    number_of_ip6=$(ip -6 addr | grep -c 'inet6 [23]')
    echo
    echo "Which IPv6 address should be used?"
    ip -6 addr | grep 'inet6 [23]' | cut -d '/' -f 1 | grep -oE '([0-9a-fA-F]{0,4}:){1,7}[0-9a-fA-F]{0,4}' | nl -s ') '
    read -p "IPv6 address [1]: " ip6_number
    until [[ -z "$ip6_number" || "$ip6_number" =~ ^[0-9]+$ && "$ip6_number" -le "$number_of_ip6" ]]; do
      echo "$ip6_number: invalid selection."
      read -p "IPv6 address [1]: " ip6_number
    done
    [[ -z "$ip6_number" ]] && ip6_number="1"
    ip6=$(ip -6 addr | grep 'inet6 [23]' | cut -d '/' -f 1 | grep -oE '([0-9a-fA-F]{0,4}:){1,7}[0-9a-fA-F]{0,4}' | sed -n "$ip6_number"p)
  fi
  echo
  echo "Which protocol should OpenVPN use?"
  echo "   1) UDP (recommended)"
  echo "   2) TCP"
  read -p "Protocol [1]: " protocol
  until [[ -z "$protocol" || "$protocol" =~ ^[12]$ ]]; do
    echo "$protocol: invalid selection."
    read -p "Protocol [1]: " protocol
  done
  case "$protocol" in
    1|"") 
    protocol=udp
    ;;
    2) 
    protocol=tcp
    ;;
  esac
  echo
  echo "What port should OpenVPN listen to?"
  read -p "Port [1194]: " port
  until [[ -z "$port" || "$port" =~ ^[0-9]+$ && "$port" -le 65535 ]]; do
    echo "$port: invalid port."
    read -p "Port [1194]: " port
  done
  [[ -z "$port" ]] && port="1194"
  echo
  echo "Select a DNS server for the clients:"
  echo "   1) Current system resolvers"
  echo "   2) Google"
  echo "   3) 1.1.1.1"
  echo "   4) OpenDNS"
  echo "   5) Quad9"
  echo "   6) AdGuard"
  read -p "DNS server [1]: " dns
  until [[ -z "$dns" || "$dns" =~ ^[1-6]$ ]]; do
    echo "$dns: invalid selection."
    read -p "DNS server [1]: " dns
  done
  echo
  echo "Enter a name for the first client:"
  read -p "Name [client]: " unsanitized_client
  # Allow a limited set of characters to avoid conflicts
  client=$(sed 's/[^0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-]/_/g' <<< "$unsanitized_client")
  [[ -z "$client" ]] && client="client"
  echo
  echo "OpenVPN installation is ready to begin."
  # Install a firewall if firewalld or iptables are not already available
  if ! systemctl is-active --quiet firewalld.service && ! hash iptables 2>/dev/null; then
    if [[ "$os" == "centos" || "$os" == "fedora" ]]; then
      firewall="firewalld"
      # We don't want to silently enable firewalld, so we give a subtle warning
      # If the user continues, firewalld will be installed and enabled during setup
      echo "firewalld, which is required to manage routing tables, will also be installed."
    elif [[ "$os" == "debian" || "$os" == "ubuntu" ]]; then
      # iptables is way less invasive than firewalld so no warning is given
      firewall="iptables"
    fi
  fi
  read -n1 -r -p "Press any key to continue..."
  # If running inside a container, disable LimitNPROC to prevent conflicts
  if systemd-detect-virt -cq; then
    mkdir /etc/systemd/system/openvpn-server@server.service.d/ 2>/dev/null
    echo "[Service]
LimitNPROC=infinity" > /etc/systemd/system/openvpn-server@server.service.d/disable-limitnproc.conf
  fi
  if [[ "$os" = "debian" || "$os" = "ubuntu" ]]; then
    apt-get update
    apt-get install -y openvpn openssl ca-certificates $firewall
  elif [[ "$os" = "centos" ]]; then
    yum install -y epel-release
    yum install -y openvpn openssl ca-certificates tar $firewall
  else
    # Else, OS must be Fedora
    dnf install -y openvpn openssl ca-certificates tar $firewall
  fi
  # If firewalld was just installed, enable it
  if [[ "$firewall" == "firewalld" ]]; then
    systemctl enable --now firewalld.service
  fi
  # Get easy-rsa
  easy_rsa_url='https://github.com/OpenVPN/easy-rsa/releases/download/v3.0.8/EasyRSA-3.0.8.tgz'
  mkdir -p /etc/openvpn/server/easy-rsa/
  { wget -qO- "$easy_rsa_url" 2>/dev/null || curl -sL "$easy_rsa_url" ; } | tar xz -C /etc/openvpn/server/easy-rsa/ --strip-components 1
  chown -R root:root /etc/openvpn/server/easy-rsa/
  cd /etc/openvpn/server/easy-rsa/
  # Create the PKI, set up the CA and the server and client certificates
  ./easyrsa init-pki
  ./easyrsa --batch build-ca nopass
  EASYRSA_CERT_EXPIRE=3650 ./easyrsa build-server-full server nopass
  EASYRSA_CERT_EXPIRE=3650 ./easyrsa build-client-full "$client" nopass
  EASYRSA_CRL_DAYS=3650 ./easyrsa gen-crl
  # Move the stuff we need
  cp pki/ca.crt pki/private/ca.key pki/issued/server.crt pki/private/server.key pki/crl.pem /etc/openvpn/server
  # CRL is read with each client connection, while OpenVPN is dropped to nobody
  chown nobody:"$group_name" /etc/openvpn/server/crl.pem
  # Without +x in the directory, OpenVPN can't run a stat() on the CRL file
  chmod o+x /etc/openvpn/server/
  # Generate key for tls-crypt
  openvpn --genkey --secret /etc/openvpn/server/tc.key
  # Create the DH parameters file using the predefined ffdhe2048 group
  echo '-----BEGIN DH PARAMETERS-----
MIIBCAKCAQEA//////////+t+FRYortKmq/cViAnPTzx2LnFg84tNpWp4TZBFGQz
+8yTnc4kmz75fS/jY2MMddj2gbICrsRhetPfHtXV/WVhJDP1H18GbtCFY2VVPe0a
87VXE15/V8k1mE8McODmi3fipona8+/och3xWKE2rec1MKzKT0g6eXq8CrGCsyT7
YdEIqUuyyOP7uWrat2DX9GgdT0Kj3jlN9K5W7edjcrsZCwenyO4KbXCeAvzhzffi
7MA0BM0oNC9hkXL+nOmFg/+OTxIy7vKBg8P+OxtMb61zO7X8vC7CIAXFjvGDfRaD
ssbzSibBsu/6iGtCOGEoXJf//////////wIBAg==
-----END DH PARAMETERS-----' > /etc/openvpn/server/dh.pem
  # Generate server.conf
  echo "local $ip
port $port
proto $protocol
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
auth SHA512
tls-crypt tc.key
topology subnet
server 10.8.0.0 255.255.255.0" > /etc/openvpn/server/server.conf
  # IPv6
  if [[ -z "$ip6" ]]; then
    echo 'push "redirect-gateway def1 bypass-dhcp"' >> /etc/openvpn/server/server.conf
  else
    echo 'server-ipv6 fddd:1194:1194:1194::/64' >> /etc/openvpn/server/server.conf
    echo 'push "redirect-gateway def1 ipv6 bypass-dhcp"' >> /etc/openvpn/server/server.conf
  fi
  echo 'ifconfig-pool-persist ipp.txt' >> /etc/openvpn/server/server.conf
  # DNS
  case "$dns" in
    1|"")
      # Locate the proper resolv.conf
      # Needed for systems running systemd-resolved
      if grep -q '^nameserver 127.0.0.53' "/etc/resolv.conf"; then
        resolv_conf="/run/systemd/resolve/resolv.conf"
      else
        resolv_conf="/etc/resolv.conf"
      fi
      # Obtain the resolvers from resolv.conf and use them for OpenVPN
      grep -v '^#\|^;' "$resolv_conf" | grep '^nameserver' | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}' | while read line; do
        echo "push \"dhcp-option DNS $line\"" >> /etc/openvpn/server/server.conf
      done
    ;;
    2)
      echo 'push "dhcp-option DNS 8.8.8.8"' >> /etc/openvpn/server/server.conf
      echo 'push "dhcp-option DNS 8.8.4.4"' >> /etc/openvpn/server/server.conf
    ;;
    3)
      echo 'push "dhcp-option DNS 1.1.1.1"' >> /etc/openvpn/server/server.conf
      echo 'push "dhcp-option DNS 1.0.0.1"' >> /etc/openvpn/server/server.conf
    ;;
    4)
      echo 'push "dhcp-option DNS 208.67.222.222"' >> /etc/openvpn/server/server.conf
      echo 'push "dhcp-option DNS 208.67.220.220"' >> /etc/openvpn/server/server.conf
    ;;
    5)
      echo 'push "dhcp-option DNS 9.9.9.9"' >> /etc/openvpn/server/server.conf
      echo 'push "dhcp-option DNS 149.112.112.112"' >> /etc/openvpn/server/server.conf
    ;;
    6)
      echo 'push "dhcp-option DNS 94.140.14.14"' >> /etc/openvpn/server/server.conf
      echo 'push "dhcp-option DNS 94.140.15.15"' >> /etc/openvpn/server/server.conf
    ;;
  esac
  echo "keepalive 10 120
cipher AES-256-CBC
user nobody
group $group_name
persist-key
persist-tun
verb 3
crl-verify crl.pem" >> /etc/openvpn/server/server.conf
  if [[ "$protocol" = "udp" ]]; then
    echo "explicit-exit-notify" >> /etc/openvpn/server/server.conf
  fi
  # Enable net.ipv4.ip_forward for the system
  echo 'net.ipv4.ip_forward=1' > /etc/sysctl.d/99-openvpn-forward.conf
  # Enable without waiting for a reboot or service restart
  echo 1 > /proc/sys/net/ipv4/ip_forward
  if [[ -n "$ip6" ]]; then
    # Enable net.ipv6.conf.all.forwarding for the system
    echo "net.ipv6.conf.all.forwarding=1" >> /etc/sysctl.d/99-openvpn-forward.conf
    # Enable without waiting for a reboot or service restart
    echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
  fi
  if systemctl is-active --quiet firewalld.service; then
    # Using both permanent and not permanent rules to avoid a firewalld
    # reload.
    # We don't use --add-service=openvpn because that would only work with
    # the default port and protocol.
    firewall-cmd --add-port="$port"/"$protocol"
    firewall-cmd --zone=trusted --add-source=10.8.0.0/24
    firewall-cmd --permanent --add-port="$port"/"$protocol"
    firewall-cmd --permanent --zone=trusted --add-source=10.8.0.0/24
    # Set NAT for the VPN subnet
    firewall-cmd --direct --add-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to "$ip"
    firewall-cmd --permanent --direct --add-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to "$ip"
    if [[ -n "$ip6" ]]; then
      firewall-cmd --zone=trusted --add-source=fddd:1194:1194:1194::/64
      firewall-cmd --permanent --zone=trusted --add-source=fddd:1194:1194:1194::/64
      firewall-cmd --direct --add-rule ipv6 nat POSTROUTING 0 -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to "$ip6"
      firewall-cmd --permanent --direct --add-rule ipv6 nat POSTROUTING 0 -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to "$ip6"
    fi
  else
    # Create a service to set up persistent iptables rules
    iptables_path=$(command -v iptables)
    ip6tables_path=$(command -v ip6tables)
    # nf_tables is not available as standard in OVZ kernels. So use iptables-legacy
    # if we are in OVZ, with a nf_tables backend and iptables-legacy is available.
    if [[ $(systemd-detect-virt) == "openvz" ]] && readlink -f "$(command -v iptables)" | grep -q "nft" && hash iptables-legacy 2>/dev/null; then
      iptables_path=$(command -v iptables-legacy)
      ip6tables_path=$(command -v ip6tables-legacy)
    fi
    echo "[Unit]
Before=network.target
[Service]
Type=oneshot
ExecStart=$iptables_path -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $ip
ExecStart=$iptables_path -I INPUT -p $protocol --dport $port -j ACCEPT
ExecStart=$iptables_path -I FORWARD -s 10.8.0.0/24 -j ACCEPT
ExecStart=$iptables_path -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
ExecStop=$iptables_path -t nat -D POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $ip
ExecStop=$iptables_path -D INPUT -p $protocol --dport $port -j ACCEPT
ExecStop=$iptables_path -D FORWARD -s 10.8.0.0/24 -j ACCEPT
ExecStop=$iptables_path -D FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT" > /etc/systemd/system/openvpn-iptables.service
    if [[ -n "$ip6" ]]; then
      echo "ExecStart=$ip6tables_path -t nat -A POSTROUTING -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to $ip6
ExecStart=$ip6tables_path -I FORWARD -s fddd:1194:1194:1194::/64 -j ACCEPT
ExecStart=$ip6tables_path -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
ExecStop=$ip6tables_path -t nat -D POSTROUTING -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to $ip6
ExecStop=$ip6tables_path -D FORWARD -s fddd:1194:1194:1194::/64 -j ACCEPT
ExecStop=$ip6tables_path -D FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT" >> /etc/systemd/system/openvpn-iptables.service
    fi
    echo "RemainAfterExit=yes
[Install]
WantedBy=multi-user.target" >> /etc/systemd/system/openvpn-iptables.service
    systemctl enable --now openvpn-iptables.service
  fi
  # If SELinux is enabled and a custom port was selected, we need this
  if sestatus 2>/dev/null | grep "Current mode" | grep -q "enforcing" && [[ "$port" != 1194 ]]; then
    # Install semanage if not already present
    if ! hash semanage 2>/dev/null; then
      if [[ "$os_version" -eq 7 ]]; then
        # Centos 7
        yum install -y policycoreutils-python
      else
        # CentOS 8 or Fedora
        dnf install -y policycoreutils-python-utils
      fi
    fi
    semanage port -a -t openvpn_port_t -p "$protocol" "$port"
  fi
  # If the server is behind NAT, use the correct IP address
  [[ -n "$public_ip" ]] && ip="$public_ip"
  # client-common.txt is created so we have a template to add further users later
  echo "client
dev tun
proto $protocol
remote $ip $port
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA512
cipher AES-256-CBC
ignore-unknown-option block-outside-dns
block-outside-dns
verb 3" > /etc/openvpn/server/client-common.txt
  # Enable and start the OpenVPN service
  systemctl enable --now openvpn-server@server.service
  # Generates the custom client.ovpn
  new_client
  echo
  echo "Finished!"
  echo
  echo "The client configuration is available in:" ~/"$client.ovpn"
  echo "New clients can be added by running this script again."
else
  clear
  echo "OpenVPN is already installed."
  echo
  echo "Select an option:"
  echo "   1) Add a new client"
  echo "   2) Revoke an existing client"
  echo "   3) Remove OpenVPN"
  echo "   4) Exit"
  read -p "Option: " option
  until [[ "$option" =~ ^[1-4]$ ]]; do
    echo "$option: invalid selection."
    read -p "Option: " option
  done
  case "$option" in
    1)
      echo
      echo "Provide a name for the client:"
      read -p "Name: " unsanitized_client
      client=$(sed 's/[^0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-]/_/g' <<< "$unsanitized_client")
      while [[ -z "$client" || -e /etc/openvpn/server/easy-rsa/pki/issued/"$client".crt ]]; do
        echo "$client: invalid name."
        read -p "Name: " unsanitized_client
        client=$(sed 's/[^0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-]/_/g' <<< "$unsanitized_client")
      done
      cd /etc/openvpn/server/easy-rsa/
      EASYRSA_CERT_EXPIRE=3650 ./easyrsa build-client-full "$client" nopass
      # Generates the custom client.ovpn
      new_client
      echo
      echo "$client added. Configuration available in:" ~/"$client.ovpn"
      exit
    ;;
    2)
      # This option could be documented a bit better and maybe even be simplified
      # ...but what can I say, I want some sleep too
      number_of_clients=$(tail -n +2 /etc/openvpn/server/easy-rsa/pki/index.txt | grep -c "^V")
      if [[ "$number_of_clients" = 0 ]]; then
        echo
        echo "There are no existing clients!"
        exit
      fi
      echo
      echo "Select the client to revoke:"
      tail -n +2 /etc/openvpn/server/easy-rsa/pki/index.txt | grep "^V" | cut -d '=' -f 2 | nl -s ') '
      read -p "Client: " client_number
      until [[ "$client_number" =~ ^[0-9]+$ && "$client_number" -le "$number_of_clients" ]]; do
        echo "$client_number: invalid selection."
        read -p "Client: " client_number
      done
      client=$(tail -n +2 /etc/openvpn/server/easy-rsa/pki/index.txt | grep "^V" | cut -d '=' -f 2 | sed -n "$client_number"p)
      echo
      read -p "Confirm $client revocation? [y/N]: " revoke
      until [[ "$revoke" =~ ^[yYnN]*$ ]]; do
        echo "$revoke: invalid selection."
        read -p "Confirm $client revocation? [y/N]: " revoke
      done
      if [[ "$revoke" =~ ^[yY]$ ]]; then
        cd /etc/openvpn/server/easy-rsa/
        ./easyrsa --batch revoke "$client"
        EASYRSA_CRL_DAYS=3650 ./easyrsa gen-crl
        rm -f /etc/openvpn/server/crl.pem
        cp /etc/openvpn/server/easy-rsa/pki/crl.pem /etc/openvpn/server/crl.pem
        # CRL is read with each client connection, when OpenVPN is dropped to nobody
        chown nobody:"$group_name" /etc/openvpn/server/crl.pem
        echo
        echo "$client revoked!"
      else
        echo
        echo "$client revocation aborted!"
      fi
      exit
    ;;
    3)
      echo
      read -p "Confirm OpenVPN removal? [y/N]: " remove
      until [[ "$remove" =~ ^[yYnN]*$ ]]; do
        echo "$remove: invalid selection."
        read -p "Confirm OpenVPN removal? [y/N]: " remove
      done
      if [[ "$remove" =~ ^[yY]$ ]]; then
        port=$(grep '^port ' /etc/openvpn/server/server.conf | cut -d " " -f 2)
        protocol=$(grep '^proto ' /etc/openvpn/server/server.conf | cut -d " " -f 2)
        if systemctl is-active --quiet firewalld.service; then
          ip=$(firewall-cmd --direct --get-rules ipv4 nat POSTROUTING | grep '\-s 10.8.0.0/24 '"'"'!'"'"' -d 10.8.0.0/24' | grep -oE '[^ ]+$')
          # Using both permanent and not permanent rules to avoid a firewalld reload.
          firewall-cmd --remove-port="$port"/"$protocol"
          firewall-cmd --zone=trusted --remove-source=10.8.0.0/24
          firewall-cmd --permanent --remove-port="$port"/"$protocol"
          firewall-cmd --permanent --zone=trusted --remove-source=10.8.0.0/24
          firewall-cmd --direct --remove-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to "$ip"
          firewall-cmd --permanent --direct --remove-rule ipv4 nat POSTROUTING 0 -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to "$ip"
          if grep -qs "server-ipv6" /etc/openvpn/server/server.conf; then
            ip6=$(firewall-cmd --direct --get-rules ipv6 nat POSTROUTING | grep '\-s fddd:1194:1194:1194::/64 '"'"'!'"'"' -d fddd:1194:1194:1194::/64' | grep -oE '[^ ]+$')
            firewall-cmd --zone=trusted --remove-source=fddd:1194:1194:1194::/64
            firewall-cmd --permanent --zone=trusted --remove-source=fddd:1194:1194:1194::/64
            firewall-cmd --direct --remove-rule ipv6 nat POSTROUTING 0 -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to "$ip6"
            firewall-cmd --permanent --direct --remove-rule ipv6 nat POSTROUTING 0 -s fddd:1194:1194:1194::/64 ! -d fddd:1194:1194:1194::/64 -j SNAT --to "$ip6"
          fi
        else
          systemctl disable --now openvpn-iptables.service
          rm -f /etc/systemd/system/openvpn-iptables.service
        fi
        if sestatus 2>/dev/null | grep "Current mode" | grep -q "enforcing" && [[ "$port" != 1194 ]]; then
          semanage port -d -t openvpn_port_t -p "$protocol" "$port"
        fi
        systemctl disable --now openvpn-server@server.service
        rm -f /etc/systemd/system/openvpn-server@server.service.d/disable-limitnproc.conf
        rm -f /etc/sysctl.d/99-openvpn-forward.conf
        if [[ "$os" = "debian" || "$os" = "ubuntu" ]]; then
          rm -rf /etc/openvpn/server
          apt-get remove --purge -y openvpn
        else
          # Else, OS must be CentOS or Fedora
          yum remove -y openvpn
          rm -rf /etc/openvpn/server
        fi
        echo
        echo "OpenVPN removed!"
      else
        echo
        echo "OpenVPN removal aborted!"
      fi
      exit
    ;;
    4)
      exit
    ;;
  esac
fi
